1. Field of the Invention
The present invention relates to an image processing device, and more particularly, to a technique extracting a paper sheet portion from an image which has been captured with the image processing device and includes a background.
2. Description of the Related Art
As a device that can read a source document made of, for example, paper, etc., an image processing device such as a scanner, a copier, a facsimile, etc. is known. Reading of a source document with such an image processing device is normally made by setting the front side (surface to be read) of a source document on the reading surface of an image reading device, and by putting a source document cover on the back side of the source document. When an image is read, light is irradiated on the front side of the set source document from the side of the reading surface, and reflected light is read with an optical reading unit (CCD) configured on the side of the reading surface. If the size of the source document is smaller than the reading surface, the source document cover (hereinafter referred to as a background) also appears around the source document viewed from the side of the reading surface. Since the background is also read in addition to the front side of the source document when the image is read, obtained image data naturally becomes data where the background appears around the source document.
Accordingly, the inventor, et al. disclosed a technique that does not require a special scheme when an image is captured, and detects an edge of a source document by using a difference between the material of a background and that of the source document only with an image process which is executed after the image is captured (Patent Document 1 implemented in FIG. 2).
[Patent Document 1] Japanese Patent Application No. 2002-370596
However, this technique has a problem that edge detection accuracy deteriorates if the material of a background and that of a source document are similar, or if an image on a background is not stable as in an image that is read with a flat-head scanner.